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Thread: String index out of range?

  1. #1
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    Default String index out of range?

    I'm supposed to be making a calculator that will add, subtract, etc. two integers. It's supposed to prompt to enter in what the person would like to do endlessly, then terminate when "exit" is entered.
    And yes, it's all supposed to be in a while loop.

    There are two problems (maybe) with my code.
    First, whenever I add, subtract, etc. the ints, it will give me a result. After the result, however, I'm getting an error saying there's a StringIndexOutofBoundsException at line 23: if(low.charAt(zero) == 'a')
    I have no idea why.
    Second, when I divide, it's returning the value as an int. I tried casting, but I couldn't get it to come out right.

    Thanks in advance.



    import java.util.Scanner;
    public class calculator
    {
        public static void main(String args[]){
     
          Scanner in = new Scanner(System.in);
          String entered,low;
          int dur = 0;
          int first, second, zero= 0;
          int answer = 0;
          String ex = "exit";
          double divide;
     
          while(dur == 0){
            System.out.println("A) Add");
            System.out.println("B) Subtract");
            System.out.println("C) Multiply");
            System.out.println("D) Divide");
            System.out.println("Enter 'exit' to close the program");
            entered = in.nextLine();
            low = entered.toLowerCase();
     
            if(low.charAt(zero) == 'a')
            {System.out.println("Enter in the first integer: ");
                first = in.nextInt();
                System.out.println("Enter in the second integer: ");
                second = in.nextInt();
                answer = add(first,second);
                System.out.println(answer);}
     
            else if(low.charAt(zero) == 'b')
            {System.out.println("Enter in the first integer: ");
                first = in.nextInt();
                System.out.println("Enter in the second integer: ");
                second = in.nextInt();
                answer= sub(first,second);
                System.out.println(answer);}
     
            else if(low.charAt(zero) == 'c')
            {System.out.println("Enter in the first integer: ");
                first = in.nextInt();
                System.out.println("Enter in the second integer: ");
                second = in.nextInt();
                answer = mult(first,second);
                System.out.println(answer);}
     
            else if(low.charAt(zero) == 'd')
            {System.out.println("Enter in the first integer: ");
                first = in.nextInt();
                System.out.println("Enter in the second integer: ");
                second = in.nextInt();
                divide = div(first,second);
                System.out.println(divide);}
     
            else if(low.equals(ex))
            {System.out.println("Ending program");
            dur = 1;}
     
            else
            {System.out.println("Invalid input. Try again.");}
          }
        }
          public static int add(int input1,int input2)
        {int sum;
        sum = (input1+input2);
        return sum;}
     
        public static int sub(int input1,int input2)
        {int equals;
        equals = (input1-input2);
        return equals;}
     
        public static int mult(int input1,int input2)
        {int prod;
        prod = (input1*input2);
        return prod;}
     
        public static double div(int input1,int input2)
        {double equ;
        equ=(input1/input2);
         return equ;}
    }


  2. #2
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    Default Re: String index out of range?

    What is the value of low when you're trying to call charAt() on it? What value are you passing in to that function? Make sure by using a debugger or adding a print statement.

    And int operations always result in an int answer, regardless of how you cast that answer. One trick is to cast the actual int values before using them in the operation, instead of trying to cast the answer after it has already been calculated.
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